Defining the Atom
Democritus
460B.C. – 570 B.C.Termed the name atom from the Greek word
“atomos”. Philosopher
If you break down an object you will eventually reach a point where you can not break it down any further. He called the smallest unit “atomos”.
John Dalton
Father of the “Atomic Theory”
1.All elements are made up of atoms.2.Atoms of an element are identical.3.Atoms of different elements combine together in
whole number ratios (you will never see a ½ or 1/3, etc.)
– i.e. H2O, CO2, C6H12O6, etc.
4.In chemical reactions, atoms are not changed, they are only rearranged. If you change atoms, it is nuclear and explosive.
Structure of Nuclear Atom
Change in Dalton’s Atomic Theory is that atoms are divisible into subatomic particles: Electrons (e-) Protons (p+) Neutrons (n0)
J.J. Thompson
Found electron by cathode ray tube.
Robert Millikan
Discovered the mass of the electron through an oil drop test.
Mass of electron = 9.11 x 10-28 g or 0.0000000000000000000000000000911 g
Too small ---- Insignificant ----Basically zero!
Food for Thought
J.J. Thompson discovered there was a negative particle called the electron. Robert Millikan discovered this negative particle has a very very small mass.
Thought: If there is a negative, there must be a positive. If electrons are so small (relatively no mass), what in
the atom makes up its mass?
Eugene Goldstein
Discovered the positively charged proton and its mass of 1 amu.
Amu = atomic mass unit
James Chadwick
Discovered the neutron with no charge and its mass of 1 amu.
Plum Pudding Model
Thompson’s Atomic ModelProtons and Electrons are randomly
dispersed throughout.
Ernest Rutherford
Gold Foil ExperimentShot positive helium
atoms through a thin gold foil. Lots of the helium cations went through and only a few deflected back.
Found there was a concentration of positive (protons). He called this concentrated spot the nucleus.
Conclusions
1. Nucleus is small.2. Nucleus is dense.3. Nucleus is positively charged.4. Atom is mainly empty space.Thus, we no longer have the Plum Pudding
Model, instead it looks like this:
The Atom
Objectives
The Atom
Three Subatomic Particles
Neutron
Proton
Electron
Neutron
Has a mass of 1Has no charge (0)Found in the nucleus
Proton
Has a mass of 1Is positively charged (+1)Determines the identity of the atomFound in the nucleus
Electron
Has NO MassIs negatively charged (-1)Found on the outside of the nucleusAtoms gain and lose electrons
Element
Elements are made of atoms with the same number of protons.
There are many elements identified and scientists have placed them on the periodic table.
How do we read the Periodic Table?
Atomic Number Number of Protons
Atomic Mass Number of Protons and Neutrons
How do we read the Periodic Table?
How do we figure out the number of neutrons?
Take the atomic mass and subtract the atomic number.
Mass (neutrons + protons) – Atomic Number (protons)
Let’s Try Together
Atomic Weight – Atomic Number
Atomic Weight = 12.01 ~ 12Atomic Number = 612 - 6 = 6 Neutrons
Now You Try!
What is the atomic mass?
137.327~137What is the atomic #?
56How many neutrons
does Barium have?137 – 56 = 81 Neutrons
Let’s Reassess Our Knowledge
What does the atomic number tell us? Number of protons.
What does the atomic mass tell us? Number of protons and neutrons.
Which subatomic particle determines the identity of the element? Proton
Which subatomic particles have mass? Neutrons and Protons
Which subatomic particle do atoms gain and lose most often? Electrons
Ions
Objectives
Ions
An ion is a charged atom that is formed when an atom gains or loses an electron. Anion
A negatively charged atom An atom gains an electron It is gaining negatives, so it becomes negative
Cation A positively charged atom An atom loses an electron It is losing negatives, so it becomes positively charged
Identifying the Type of Ions
Ca+2
O-2
U6+
Sn4+
N-3
Cation
Anion
Cation
Cation
Anion
Lost Electrons
Gained Electrons
Lost Electrons
Lost Electrons
Gained Electrons
2
2
6
4
3
Determining the Number of Electrons
Ion Protons Gain or Lose
Electrons
Electrons Neutrons
Ca+2 20 Lose 18 20
O-2 8 Gain 10 8
U6+ 92 Lose 86 146
Sn4+ 50 Lose 46 69
N-3 7 Gain 10 7
Isotopes
Objectives
Isotopes
Atoms with the same number of protons, but a different number of neutrons.
Same element with a different atomic mass.
Carbon Isotopes
Determining the Number of Neutrons
Remember: To find the number of neutrons, you must take the atomic mass and subtract the atomic number.
Another way to write the element: Element Symbol – Atomic Mass C - 12
Determine the Neutrons in the Isotopes: Li-6 Li-7
6-3 = 3 Neutrons
7-3 = 4 Neutrons
Other Ways to Write
Carbon-12Carbon-13Carbon-14
C C C
12
14
13
Atomic Mass
6
6
6
Atomic NumberC
Average Atomic Mass
Objectives
Average Atomic Mass
Why does the mass have numbers after the decimal?
Elements contain atoms with different masses.
Same number of protons, but different number of neutrons (isotopes of the same element).
What is Average Atomic Mass?
Average Atomic mass Average of all atoms with the same number of
protons. Thus, it is the average of isotopes for that element.
Abundance Amount of that isotope in nature. Displayed in percentage.
How Do We Determine the Average Atomic Mass?
1. Write the abundance and the corresponding isotope mass.
2. Rewrite the percent abundance as a decimal by moving the decimal two places to the left.
3. Multiply abundance (decimal) of that isotope by the mass.
4. Repeat step 1-3 for all isotopes.5. Add all the numbers together.
Lets Try Together
Calculate the average atomic mass of iron if its abundance in nature is 15% iron-55 and 85% iron-56.
15% iron-55
85% iron-56
0.15
0.85 0.85 x 56
0.15 x 55 8.25
47.655.85 amu8.25 + 47.6
1. Write the percent abundance and corresponding isotope mass.
2. Rewrite the percent abundance as a decimal.
3. Multiply abundance (decimal) by the isotope mass.
4. Add the numbers together.
In-Class Practice #2
What is the average atomic mass of silicon if 92.21% of its atoms have a mass of 27.977 amu, 4.07% have a mass of 28.976 amu, and 3.09% have a mass of 29.974 amu?
92.21% Si-27.977
4.07% Si-28.976
3.09% Si-29.974
.9221
.0407
.0309
.9221 x 27.977
.0407 x 28.976
.0309 x 29.974
25.7975917
1.1793232
0.9261966
25.7975917 1.1793232+ 0.9261966 27.903 amu
1. Write the percent abundance and corresponding isotope mass.
2. Rewrite the percent abundance as a decimal.
3. Multiply abundance (decimal) by the isotope mass.
4. Add the numbers together.
In-Class Practice #3
Calculate the average atomic mass for neon if its abundance in nature is 90.5% neon-20 (19.922 amu), 0.3% neon-21 (20.994 amu), and 9.2% neon-22 (21.991 amu).
90.5% 19.922
9.2% 21.991
0.3% 20.994
0.905
0.003
0.092
0.905 x 19.922
0.003 x 20.994
0.092 x 21.991
18.02941
0.062982
2.023172
18.02941 0.062982+ 2.023172 20.116 amu
In-Class Practice #4
Calculate the average atomic mass of chromium.
4.35% 49.946
2.35% 53.939
83.8% 51.941
9.5% 52.941
x 49.946
x 51.941
x 52.941
x 53.939
0.0435
0.838
0.095
0.0235
2.172651
43.526558
5.029395
1.2675665
51.996 amu
Now You Try on Your Own!
Independent Practice On Average Atomic Mass
Nuclear Chemistry
Objectives
1. Define nuclear chemistry.2. Describe the two forces in the nucleus.3. Explain why nuclear reactions occur.4. Name five types of nuclear decay.
Nuclear Chemistry
Nuclear Chemistry Study of changes in structure of nuclei and
subsequent changes in chemistry.
When a nucleus spontaneously changes it structure and emits radiation, we call this radioactive nuclei.
What is in the nucleus?
Protons and Neutrons
Nuclear Versus Chemical Reactions
Differences between nuclear and chemical reactions. Involves the nucleus and not electrons Much larger release in energy in nuclear reaction. Nuclear reaction produces different elements. Rate of nuclear reaction not dependent upon the
chemical environment.
Nucleus
Nucleus Has two nucleons, protons and neutrons. Protons are positively charged. Neutrons are neutral or have no charge. The overall charge of the nucleus is positive.
But, what holds these nucleons (subatomic particles in the nucleus) together when there are so many positively charged particles in a small, dense space.
Wouldn’t they repel each other and fly apart?
Two Types of Forces
1. Electrostatic Force2. Strong Force
Electrostatic Force
Force that causes oppositely charged particles to attract/repel. Any element with more than 1 proton will have
electrostatic repulsion between the protons.
Strong Force
The force between the nucleons (protons and neutrons).
Keeps the nucleus from flying apartThe neutrons increase the strong force with
out increasing electrostatic repulsion between nucleons (the protons).
Neutron-Proton Ratios
Neutrons play a key role stabilizing the nucleus.
Therefore, the ratio of neutrons to protons is an important factor.
Neutron- Proton Ratio
Smaller nuclei are more stable because they have a neutron-to-proton ratio close to 1:1.
Small Nuclei Atomic number is less
than or equal to 20 Z 20
Neutron- Proton Ratio
As nuclei get larger (more protons = more repulsion), it takes a greater number of neutrons to stabilize the nucleus.
Belt of Stability
The shaded region in the figure shows what nuclides would be stable, the so-called belt of stability.
Radioactivity
If a nuclei is unstable (off the line of stability) it will decay in order for it to become stable again.
• Radioactive decay • Process in which a nucleus
spontaneously disintegrates, giving off radiation.
Types of Radioactive Decay
Objectives
Five Types of Radioactive Decay
1. Alpha Decay2. Beta Decay3. Gamma Emission4. Positron Emission5. Electron Capture
Alpha Decay
Loss of an -particle (a helium nucleus)
He42
U23892 Th
23490 He
42+
Beta Decay
Loss of a -particle (a high energy electron)
0
−1 e0
−1or
I13153 Xe
13154 + e0
−1
Gamma Emission
Loss of a -ray (high-energy radiation that almost always accompanies the loss of a
nuclear particle)
00
Positron Emission
Loss of a positron (a particle that has the same mass as but opposite charge than an
electron)
e0
+1
C11
6 B11
5 + e0
+1
Electron Capture/ K-Capture
Addition of an electron to a proton in the nucleus As a result, a proton is transformed into a neutron.
p11 + e
0−1 n
10
Writing and Balancing Nuclear Reactions
Objectives
1. Describe the difference between decay and capture.
2. Identify the type of decay in a reaction.3. Balance nuclear reactions.4. Predict the type of decay an atom will
undergo.
Nuclei above this belt have too many neutrons.
They tend to decay by emitting beta particles.
Stable Nuclei
Nuclei below the belt have too many protons.
They tend to become more stable by positron emission or electron capture.
Stable Nuclei
There are no stable nuclei with an atomic number greater than 83.
These nuclei tend to decay by alpha emission.
How Do We Identify Type of Nuclear Decay
1. Look for decay particles.
2. Emitted particles (decay) are on the right hand side of the arrow.
3. Captured particles are on the Left hand side of the arrow.
He42 e
0+1
0−1 e0
−1or 00
Decay
Captured
Let’s Try Together!
____ +_____
____ +_____
____ +_____
____ +_____
____ + _______
He42
e0
−1
e0
+1
00
e 0
−1
Write Nuclear Reactions
Uranium-235 undergoes alpha decay
235
92U 4
2He + 231
90Th
Predicting the Type of Decay
Objectives
Predict Type of Decay
If Atomic Number is greater than 83• Nucleus is too big• Undergoes alpha decay
Too many protons and neutrons Best way to get rid of the nucleons is to get rid of an
alpha particle or helium nucleus. This will remove 2 protons and 2 neutrons and reduce
the size of the nucleus.
Predict Type of Decay
If Atomic mass is greater than the periodic table. • Too many neutrons
• Above belt of Stability• Undergoes Beta decay To get rid of the neutron, the atom will split it into a
proton and electron.
o1n +-1
1p + -10e
The proton stays in the nucleus increasing the atomic number (changing the element) and releases the electron.
This reduces the # of neutrons and increases # of protons.
Predict Type of Decay
Atomic mass less than on the periodic table. oToo few neutrons or too many protons
Below belt of StabilityoTherefore positron emission or electron capture
Examples: 261104Rf, 57
25Mn, 116C
The atom will capture an electron and combine it with a proton to form a neutron. This decreases the # of protons and increases the # of neutrons. (electron capture)
-11p + -1
0e o1n
The atom will release a positron (positive electron) to reduce the number of protons and increase the number of neutrons.
Balance Nuclear Reactions
10n + 235
92U → 2 10n + 97
40Zr+ 13752Te
Balance Nuclear Reactions
84218Po 2
4He + ________
99253Es + 2
4He 01n + _________
61142Pm + ______ 60
142Nd
Importance of Radiation
Objectives
How Does This Effect US?
Alpha particles are large and are stopped by a piece of paper.
Beta particles are smaller. An aluminum plate will stop them.
Gamma radiation needs 4 meters of lead to be stopped because they have no mass or charge. Tungsten and its alloys
can stop gamma with less mass.
Energy in Nuclear Reactions
There is a tremendous amount of energy stored in nuclei.
Einstein’s famous equation, E = mc2, relates directly to the calculation of this energy. Mass is converted into Energy.
In chemical reactions the amount of mass converted to energy is minimal.
However, these energies are many thousands of times greater in nuclear reactions.
Uses of Radiation
Radiation is used in Medicine Academics Industry (generating electricity) Applications in
Agriculture Archaeology (carbon dating) Space exploration Law enforcement Geology (including mining) and many others
Medical Uses
X-rays Move through skin, but not bone because it is denser.
The shadow of the bones is printed on a film.
Radiation Therapy (detection/ treatment) Reduce tumors and treat cancer
Nuclear medicine to diagnose clinical conditions Conditions in kidney, pancreas, thyroid, liver and
brain. Use radioactive iodine for thyroid
Industrial
X-rays used to disinfect medical equipment (bandages, syringes, and surgical instruments) and food to make it much longer until it spoils.
Ultraviolet is used in some homes to disinfect their water supply. Nonstick cookware is treated with gamma rays to prevent our food
from sticking. Our clothes are treated with radiation before wrinkle-free and soil-
releasing chemicals on it. Polyethylene shrinkwrap has been treated with radiation so that
it can be heated above its usual melting point and wrapped around the foods to provide an airtight protective covering.
Radiation can be used to control insect populations, thereby decreasing the use of dangerous pesticides
Nuclear PowerPlants
Use fission and fusion to create energy
Half-Life
Objectives
Radioactive Decay Series
Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation.
They undergo a series of decays until they form a stable nuclide (often a nuclide of lead).
Radioactive Decay Series
Half-Life
Half-life (t½)– Time required for half the atoms of a
radioactive nuclide to decay.– Shorter half-life = less stable.
20 g
10 g5 g
2.5 g
after 1 half-life
Start after 2 half-lives
after 3 half-lives
Half-Life
1.00 mg
0.875 mg
0.500 mg
0.250 mg0.125 mg
8.02 days0.00 days 16.04 days 24.06 days
131 53 I
131 53 I
0.500 mg0.750 mg131
54 Xe
I131
53 Xe131
540
-1+ +
Half-Life
0 1 2 3 4Number of half-lives
Rad
iois
otop
e re
mai
ning
(%
)
100
50
25
12.5
Half-life of Radiation
Initial amountof radioisotope
t1/2
t1/2
t1/2
After 1 half-life
After 2 half-lives
After 3 half-lives
Half-Life PlotA
mou
nt o
f Io
dine
-131
(g)
20
15
10
5
0
40 48 560 8
1 half-life
16
2 half-lives
24
3 half-lives
32
4 half-lives etc…
Time (days)
Half-life of iodine-131 is 8 days
Half-Life of Isotopes
Isotope Half-Live Radiation emitted
Half-Life and Radiation of Some Naturally Occurring Radioisotopes
Carbon-14 5.73 x 103 years
Potassium-40 1.25 x 109 years
Thorium-234 24.1 days
Radon-222 3.8 days
Radium-226 1.6 x 103 years
Thorium-230 7.54 x 104 years
Uranium-235 7.0 x 108 years
Uranium-238 4.46 x 109 years
How Much Remains?
After oneone half-life, of the original atoms remain.
After twotwo half-lives, ½ x ½ = 1/(22) = of the original atoms remain.
After threethree half-life, ½ x ½ x ½ = 1/(23) = of the original atoms remain.
After fourfour half-life, ½ x ½ x ½ x ½ = 1/(24) = of the original atoms remain.
After fivefive half-life, ½ x ½ x ½ x ½ x ½ = 1/(25) = of the original atoms remain.
After sixsix half-life, ½ x ½ x ½ x ½ x ½ x ½ = 1/(26) = of the original atoms remain.
14
12
18
116
132
164
1 half-life 2 half-lives 3 half-lives
12
14 1
8 116 1
32 164 1
128
Accumulating“daughter”
isotopes
4 half-life 5 half-lives 6 half-lives 7 half-lives
Surviving“parent”isotopes
Beginning
Fraction remaining = 1/(2n).
The iodine-131 nuclide has a half-life of 8 days. If you originally have a 625-g sample, after 2 months you will have approximately?
a. 40 gb. 20 gc. 10 gd. 5 ge. less than 1 g
625 g 312 g 156 g 78 g 39 g 20 g 10 g 5 g 2.5 g1.25 g
0 d 8 d 16 d 24 d 32 d 40 d 48 d 56 d 64 d 72 d
0 1 2 3 4 5 6 7 8 9
Data Table: Half-life Decay~ Amount Time # Half-Life
Assume 30 days = 1 month
60 days8 days = 7.5 half-life(s)
A = Ao(1/2)n
A = amount remainingAo = original amountn = # of half-life(s)
N = (625 g)(1/2)7.5
N = 3.45 g
Let’s Practice Together!
The half-life of carbon-14 is 5730 years. If a sample originally contained 3.36 g of C-14, how much is present after 22,920 years?
0.21 g C-14
Gold-191 has a half-life of 12.4 hours. After one day and 13.2 hours, 10.6 g of gold-19 remains in a sample. How much gold-191 was originally present in the sample?84.8 g Au-191
There are 3.29 g of iodine-126 remaining in a sample originally containing 26.3 g of iodine-126. The half-life of iodine-126 is 13 days. How old is the sample?
39 days old
A sample that originally contained 2.5 g of rubidium-87 now contains 1.25 g. The half-life of rubidium-87 is 6 x 1010 years. How old is the sample? Is this possible? Why or why not?
6 x 1010 years
22,930 years
The half-life of carbon-14 is 5730 years. If a sample originally contained 3.36 g of C-14, how much is present after 22,920 years?
3.36 g 1.68 g 0.84 g 0.42 g 0.21 g
0 y 5,730 y 11,460 y 17,190 y 22,920 y
0 1 2 3 4
Data Table: Half-life DecayAmount Time # Half-Lifet1/2 = 5730 years
n = 5,730 years
n = 4 half-life
(4 half-life)(5730 years) = age of sample
(# of half-life)(half-life) = age of sample
22,920 years
Fusion and Fission
Objectives
Nuclear Fission
A large nucleus is bombarded with a small particle.
Nucleus splits into smaller nuclei and several neutrons.
Large amounts of energy are released.
Nuclear Chain Reaction
Bombardment of the radioactive nuclide with a neutron starts the process.
Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons.
This process continues in what we call a nuclear chain reaction.
If there are not enough radioactive nuclides in the path of the ejected neutrons, the chain reaction will die out.
Nuclear Fusion
occurs at extremely high temperatures (100 000 000°C). Why?
combines small nuclei into larger nuclei.releases large amounts of energy.occurs continuously in the sun and stars.
Nuclear Fusion
This type of Fusion is beingExamined asAn alternativeEnergy sourceOn Earth.
Nuclear Fusion
Fusion would be a superior method of generating power. The good news is that the
products of the reaction are not radioactive.
The bad news is that in order to achieve fusion, the material must be in the plasma state at several million kelvins.
Tokamak apparati like the one shown at the right show promise for carrying out these reactions.
They use magnetic fields to heat the material.